linux-kernel - Re: [PATCH v3] can: m_can: add support for one shot mode

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Message-ID: <38ade7ff-0e0c-afe9-a927-17317f0f27b9@pengutronix.de>
Date:   Wed, 6 Nov 2019 11:34:26 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Pankaj Sharma <pankj.sharma@...sung.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     wg@...ndegger.com, davem@...emloft.net,
        eugen.hristev@...rochip.com, ludovic.desroches@...rochip.com,
        pankaj.dubey@...sung.com, rcsekar@...sung.com,
        Sriram Dash <sriram.dash@...sung.com>
Subject: Re: [PATCH v3] can: m_can: add support for one shot mode

On 10/21/19 2:04 PM, Pankaj Sharma wrote:
> According to the CAN Specification (see ISO 11898-1:2015, 8.3.4
> Recovery Management), the M_CAN provides means for automatic
> retransmission of frames that have lost arbitration or that
> have been disturbed by errors during transmission. By default
> automatic retransmission is enabled.
> 
> The Bosch MCAN controller has support for disabling automatic
> retransmission.
> 
> To support time-triggered communication as described in ISO
> 11898-1:2015, chapter 9.2, the automatic retransmission may be
> disabled via CCCR.DAR.
> 
> CAN_CTRLMODE_ONE_SHOT is used for disabling automatic retransmission.
> 
> Signed-off-by: Pankaj Sharma <pankj.sharma@...sung.com>
> Signed-off-by: Sriram Dash <sriram.dash@...sung.com>
> ---
> 
> changes in v3: 
> - resolving build errors for net-next branch
> 
> changes in v2:
> - rebase to net-next
> 
>  drivers/net/can/m_can/m_can.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
> index 562c8317e3aa..75e7490c4299 100644
> --- a/drivers/net/can/m_can/m_can.c
> +++ b/drivers/net/can/m_can/m_can.c
> @@ -123,6 +123,7 @@ enum m_can_reg {
>  #define CCCR_CME_CANFD_BRS	0x2
>  #define CCCR_TXP		BIT(14)
>  #define CCCR_TEST		BIT(7)
> +#define CCCR_DAR		BIT(6)
>  #define CCCR_MON		BIT(5)
>  #define CCCR_CSR		BIT(4)
>  #define CCCR_CSA		BIT(3)
> @@ -1135,7 +1136,7 @@ static void m_can_chip_config(struct net_device *dev)
>  	if (cdev->version == 30) {
>  	/* Version 3.0.x */
>  
> -		cccr &= ~(CCCR_TEST | CCCR_MON |
> +		cccr &= ~(CCCR_TEST | CCCR_MON | CCCR_DAR |
>  			(CCCR_CMR_MASK << CCCR_CMR_SHIFT) |
>  			(CCCR_CME_MASK << CCCR_CME_SHIFT));
>  
> @@ -1145,7 +1146,7 @@ static void m_can_chip_config(struct net_device *dev)
>  	} else {
>  	/* Version 3.1.x or 3.2.x */
>  		cccr &= ~(CCCR_TEST | CCCR_MON | CCCR_BRSE | CCCR_FDOE |
> -			  CCCR_NISO);
> +			  CCCR_NISO | CCCR_DAR);
>  
>  		/* Only 3.2.x has NISO Bit implemented */
>  		if (cdev->can.ctrlmode & CAN_CTRLMODE_FD_NON_ISO)
> @@ -1165,6 +1166,10 @@ static void m_can_chip_config(struct net_device *dev)
>  	if (cdev->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)
>  		cccr |= CCCR_MON;
>  
> +	/* Disable Auto Retransmission (all versions) */
> +	if (cdev->can.ctrlmode & CAN_CTRLMODE_ONE_SHOT)
> +		cccr |= CCCR_DAR;
> +
>  	/* Write config */
>  	m_can_write(cdev, M_CAN_CCCR, cccr);
>  	m_can_write(cdev, M_CAN_TEST, test);
> @@ -1310,7 +1315,8 @@ static int m_can_dev_setup(struct m_can_classdev *m_can_dev)
>  	m_can_dev->can.ctrlmode_supported = CAN_CTRLMODE_LOOPBACK |
>  					CAN_CTRLMODE_LISTENONLY |
>  					CAN_CTRLMODE_BERR_REPORTING |
> -					CAN_CTRLMODE_FD;
> +					CAN_CTRLMODE_FD |
> +					CAN_CTRLMODE_ONE_SHOT;
>  
>  	/* Set properties depending on M_CAN version */
>  	switch (m_can_dev->version) {

What happens if you have called netif_stop_queue() and the controller
was not able to send a single frame?

What happens to the echo_skb, if the controller was not able to send a
frame?

Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
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